Galvanic cells may generate large quantities of gas under certain conditions during use. Since many such cells are required to be tightly sealed in order to prevent loss of electrolyte by leakage, high internal gas pressures may develop. Such pressures may cause leakage, bulging or possible rupture of the cell container under abusive conditions, if not properly vented. If a vent valve is employed, it must be resealable in order to avoid drying out of the electrolyte over the life of the cell and to prevent ingress of oxygen and moisture from the atmosphere which can cause wasteful corrosion of the anode.
In the past, several different types of resealable pressure relief vent valves have been used for releasing high internal gas pressures from inside a sealed galvanic cell. One type of valve that has been commonly used consists basically of a valve member such as a flat rubber gasket which is biased into sealing position over a vent orifice by means of a resilient member such as a helical spring. The resilient member or spring is designed to yield at a certain predetermined internal gas pressure so as to momentarily break the seal and allow the gas to escape through the vent orifice.
In U.S. Pat. No. 3,664,878, to Author issued on May 23, 1972, a resealable vent is disclosed which comprises a resilient deformable ball of elastomeric material positioned to overlie a vent orifice provided within the cell's container. A retainer means is positioned over the resilient ball for maintaining the ball in place over the vent orifice and in contact with a valve seat provided around the peripheral edge portions of the vent orifice and for compressing and deforming the resilient ball into a flattened configuration forming a normally fluid-tight seal between the flattened ball and the valve seat. The resilient ball is capable of undergoing further temporary deformation upon the build up of a predetermined high internal gas pressure inside the container so as to momentarily break the seal and allow gas to escape through the vent orifice.
However, with the continuing development of portable electrically powered devices such as tape recorders and play-back machines, radio transmitters and receivers, and the like, a new type of reliable, long service life cells or batteries has been developed. These newly developed electrochemical cell systems provide a long service life by utilizing highly reactive anode materials such as lithium, sodium and the like, in conjunction with high energy density nonaqueous liquid cathode materials and a suitable salt.
It has recently been disclosed in the literature that certain materials are capable of acting both as an electrolyte carrier, i.e., as solvent for the electrolyte salt, and as the active cathode for a nonaqueous electrochemical cell. U.S. application Ser. No. 439,521 by G. E. Blomgren et al filed Feb. 4, 1974, which is a continuation-in-part of application Ser. No. 212,582 filed on Dec. 27, 1971, discloses a nonaqueous electrochemical cell comprising an anode, a cathode collector and a cathode-electrolyte, said cathode-electrolyte comprising a solution of an ionically conductive solute dissolved in an active cathode depolarizer wherein said active cathode depolarizer comprises a liquid oxyhalide of an element of Group V or Group VI of the Periodic Table. The "Periodic Table" is the Periodic Table of Elements as set forth on the inside back cover of the Handbook of Chemistry and Physics, 48th Edition, the Chemical Rubber Co.. Cleveland, Ohio, 1967-1968. For example, such nonaqueous cathode materials would include sulfuryl chloride, thionyl chloride, phosphorus oxychloride, thionyl bromide, chromyl chloride, vanadyl tribromide and selenium oxychloride.
Another class of liquid cathode materials would be the halides of an element of Group IV to Group VI of the Periodic Table. For example, such nonaqueous cathode materials would include sulfur monochloride, sulfur monobromide, selenium tetrafluoride, selenium monobromide, thiophosphoryl chloride, thiophosphoryl bromide, vanadium pentafluoride, lead tetrachloride, titanium tetrachloride, disulfur decafluoride, tin bromide trichloride, tin dibromide dichloride and tin tribromide chloride.
It has been found that when employing high energy density liquid cathode materials in nonaqueous cell systems, the cells exhibit higher voltage than cells employing conventional aqueous systems which results in fewer cell units being required to operate a particular battery-powered device. In addition, many of the oxyhalide and halide nonaqueous cells display relatively flat discharge voltage-versus-time curves. Thus these cells can be employed to produce batteries that will provide a working voltage closer to a designated cut-off voltage than is practicable with some conventional aqueous systems which generally do not exhibit flat discharge voltage-versus-time curves.
However, one possible disadvantage in the use of oxyhalide and halide liquid cathode nonaqueous cells is that it may be possible that during storage or use, some of the oxyhalide, halide or their reaction products may escape from the cell. This escape of liquids and/or gases could cause damage to the device employing the cell or to the surface of a compartment or shelf where the cell is stored. On the other hand, if the seal of the cell is effectively permanently secured, then it is possible that the build up of internal pressure within the cell could cause the cells container to rupture. To prevent rupture of the cell's container from possible internal pressure build up, it is thus necessary to vent the cell at some predetermined pressure. It has been reported that some oxyhalides such as thionyl chloride and sulfuryl chloride should be vented at pressures below about 500 psi and preferably between about 150 and 300 psi.
It is, therefore, an important object of this invention to provide a low pressure resealable vent closure for electrochemical cells, specifically oxyhalide cells.
It is another object of this invention to provide a low pressure resealable vent closure for small size cylindrical cells employing, for example, oxyhalides as the active cathodic material.
It is another object of this invention to provide a low pressure resealable vent closure for nonaqueous cells that is inexpensive to manufacture and easy to assemble.
It is another object of this invention to provide a method for assembling a low pressure resealable vent closure on electrochemical cells.
It is another object of this invention to provide a method for assembling the solid components of the cell in a container followed by closing the container with a cover and then adding the liquid components of the cell prior to assembling the low pressure resealable vent closure of this invention onto the cell's housing.
The foregoing and additional objects will become fully apparent from the following description and the accompanying drawings.